When he isn’t directing documentaries like “The Thin Blue Line” or the Oscar-winning “Fog of War,” or writing books about the Jeffrey MacDonald case (“A Wilderness of Error”), or making commercials for such corporations as Exxon, Nike, and Cisco, Errol Morris manages still to be busy. The Cambridge filmmaker’s latest creation is a series of short films for ESPN called “It’s Not Crazy, It’s Sports.” The series premieres Sunday on the all-sports network and the rest will be posted on ESPN’s Grantland website next week. As you might expect of Morris, the subjects of the shorts are a bit offbeat, including the mascot Mr. Met and memorabilia collectors who purchased, oh, Ty Cobb’s dentures and the toilet from the Toronto Maple Leafs locker room. The idea for the series was hatched after Morris made a commercial for ESPN that featured a Brooklyn, N.Y., funeral parlor where the deceased are buried in their sports gear. “These aren’t traditional sports stories, but human stories with an existential, maybe even philosophical dimension,” Morris told us Thursday. “The Mr. Met one is one my favorite things I’ve ever done.”